On the relationship between black hole mass and X-ray variability amplitude in the low-mass regime of active galactic nuclei

摘要

Recent studies of active galactic nuclei (AGN) found a statistical inverse scaling between the X-ray normalized excess variance σ_(rms)~2 (variability amplitude) and the black hole mass spanning over Mbh = 10~6 — 10~9 M_⊙. We present a study of this relation by including AGN with Mbh = 10~5 — 10~6 M_⊙. It is found that the relation is no longer a simple extrapolation of the known inverse proportion, but starts to flatten around 10~6 M_⊙. This behavior can be understood by the shape of the power spectrum density of AGN and its dependence on the black hole mass.